Recently, chemical amplification type DUV (deep ultra violet) photoresists have proven to be useful to achieve high sensitivity in processes for preparing microcircuits in the manufacture of semiconductors. These photoresists are prepared by blending a photoacid generator with polymer matrix macromolecules having acid labile structures.
According to the reaction mechanism of such a negative photoresist, the photoacid generator generates acid when it is irradiated by the light source, and the main chain or branched chain of the polymer matrix macromolecule is cross-linked with the generated acid to form a cross-linked structure. Thus, the portion exposed to light cannot be dissolved by developing solution and remains unchanged, thereby producing a negative image of a mask on the substrate. In the lithography process, resolution depends upon the wavelength of the light source - the shorter the wavelength, the smaller the pattern that can be formed. However, when the wavelength of the light source is decreased in order to form a micro pattern [for example, in the case of using 193 nm wavelength or EUV (extremely ultraviolet) light], it is disadvantageous in that the lens of the exposing device is deformed by the light source, thereby shortening its life.
Melamine, a conventional cross-linker, has a limited number (three) of functional groups which can form a cross-linkage with acid. Further, a large amount of acid must be generated when melamine is used as a cross-linker, because acid is consumed by the cross-linking reaction. As a result, high-energy light exposure is required for such cross-linking agents.
In order to overcome the disadvantages described above, chemical amplification type compounds that cross-link with a photoresist polymer (also referred to herein as a "photoresist resin") and use less amounts of energy are desirable. However, such chemical amplification type cross-linkers have not yet been developed.